Switching circuit with gate driver having precharge period and method therefor

Abstract

A switching circuit includes first and second transistors, and a driver circuit. The first transistor has a first current electrode coupled to a first power supply voltage terminal, a second current electrode, and a control electrode. The second transistor has a first current electrode coupled to the second current electrode of the first transistor, a second current electrode coupled to a second power supply voltage terminal, and a control electrode. The driver circuit has an input for receiving an input signal, and an output coupled to the control electrode of the first transistor. The driver circuit precharges the control electrode of the first transistor to a first predetermined voltage, and in response to the input signal transitioning from a first logic state to a second logic state, the driver circuit provides a second predetermined voltage to the control electrode of the first transistor to cause the first transistor to be conductive.

1. A switching circuit comprising:
 a first transistor having a first current electrode coupled to a first power supply voltage terminal, a second current electrode, and a control electrode; 
 a second transistor having a first current electrode coupled to the second current electrode of the first transistor, a second current electrode coupled to a second power supply voltage terminal, and a control electrode; and 
 a first driver circuit having an input for receiving an input signal, and an output coupled to the control electrode of the first transistor, the first driver circuit for precharging the control electrode of the first transistor to a first predetermined voltage, the first driver circuit comprising a first comparator, and in response to the comparator sensing that a voltage at the control electrode of the first transistor is equal to a first voltage level, causing the precharginq of the control electrode of the first transistor to be stopped at the first predetermined voltage, and in response to the input signal transitioning from a first logic state to a second logic state, the first driver circuit providing a second predetermined voltage to the control electrode of the first transistor to cause the first transistor to be conductive. 
 
     
     
       2. The switching circuit of  claim 1 , wherein the first predetermined voltage is equal to approximately a threshold voltage of the first transistor. 
     
     
       3. The switching circuit of  claim 1 , further comprising a second driver circuit having an output coupled to the control electrode of the second transistor. 
     
     
       4. The switching circuit of  claim 1 , wherein the second predetermined voltage is above a power supply voltage provided to the first power supply voltage terminal. 
     
     
       5. The switching circuit of  claim 1 , further comprising a second comparator for sensing when the voltage at the control electrode of the second transistor is equal to or less than a second voltage level, and in response, causing the control electrode of the first transistor to receive the second predetermined voltage. 
     
     
       6. The switching circuit of  claim 5 , wherein the second comparator further comprises an output coupled to an input of the first driver circuit. 
     
     
       7. The switching circuit of  claim 1 , further comprising:
 a third transistor having a first current electrode coupled to the first power supply voltage terminal, a control electrode coupled to the control electrode of the first transistor, and a second current electrode coupled to an input of the first comparator; and 
 a resistive element having a first terminal coupled to the second current electrode of the third transistor, and a second terminal coupled to the second power supply voltage terminal. 
 
     
     
       8. The switching circuit of  claim 1 , further comprising:
 a current source having a first terminal coupled to the first power supply voltage terminal, and a second terminal; 
 a switch having a first terminal coupled to the second terminal of the current source, a control terminal coupled to receive a control signal, and a second terminal; and 
 a bootstrap capacitor having a first plate electrode coupled to the second terminal of the switch, and a second plate electrode coupled to the second current electrode of the first transistor. 
 
     
     
       9. A switching circuit configured as a half bridge, the switching circuit comprising:
 a high side transistor having a first current electrode coupled to a first power supply voltage terminal, a second current electrode, and a control electrode; 
 a low side transistor having a first current electrode coupled to the second current electrode of the high side transistor, a second current electrode coupled to a second power supply voltage terminal, and a control electrode; 
 a high side driver circuit having an input for receiving an input signal, and an output coupled to the control electrode of the high side transistor, the high side driver circuit for precharging the control electrode of the high side transistor to a first predetermined voltage, and in response to the input signal transitioning from a first logic state to a second logic state, the high side driver circuit providing a second predetermined voltage to the control electrode of the high side transistor to cause the high side transistor to be conductive; 
 a comparator having a first input terminal coupled to the control electrode of the low side transistor, a second input terminal coupled to a voltage source, and an output terminal for providing a logic signal in response to detecting that a voltage at the control electrode of the low side transistor has decreased to be equal to or below a voltage of the voltage source; and 
 a low side driver circuit having an input for receiving the input signal, and an output coupled to the control electrode of the low side transistor. 
 
     
     
       10. The switching circuit of  claim 9 , further comprising a comparator having a first input terminal coupled to the control electrode of the high side transistor, a second input terminal coupled to a sensing circuit, and an output terminal, wherein the comparator provides a logic signal in response to sensing that the first predetermined voltage has been reached. 
     
     
       11. The switching circuit of  claim 9 , further comprising:
 a current source having a first terminal coupled to the first power supply voltage terminal, and a second terminal; 
 a switch having a first terminal coupled to the second terminal of the current source, a control terminal coupled to receive the logic signal from the comparator, and a second terminal; and 
 a bootstrap capacitor having a first plate electrode coupled to the second terminal of the switch, and a second plate electrode coupled to the second current electrode of the high side transistor. 
 
     
     
       12. The switching circuit of  claim 9 , wherein the high side transistor and the low side transistor are both characterized as being power NMOS transistors. 
     
     
       13. The switching circuit of  claim 9 , wherein the first predetermined voltage is equal to approximately a threshold voltage of the high side transistor. 
     
     
       14. In a switching circuit having a high side transistor coupled to a low side transistor in a half bridge configuration, a method comprising:
 precharging a control electrode of the high side transistor to a first predetermined voltage while the low side transistor is conductive; 
 detecting when the control electrode of the high side transistor has been precharged to the first predetermined voltage, and in response, stopping the precharging; 
 causing the low side transistor to become substantially non-conductive; and 
 sensing when the low side transistor becomes substantially non-conductive, and in response, driving the control electrode of the high side transistor with a second predetermined voltage to cause the high side transistor to be conductive. 
 
     
     
       15. The method of  claim 14 , wherein the first predetermined voltage is equal to approximately a threshold voltage of the high side transistor. 
     
     
       16. The method of  claim 14 , wherein precharging the control electrode of the high side transistor further comprises precharging the control electrode using a power supply voltage. 
     
     
       17. The method of  claim 16 , wherein driving the control electrode of the high side transistor with a second predetermined voltage further comprises driving the control electrode of the high side transistor using a third predetermined voltage, wherein the third predetermined voltage is higher than the power supply voltage.